Peel and slice the ginger root into ⅛ inch slices. A mandolin makes this step simple and keeps the thickness even.
Add the sliced ginger to a medium pot and cover with water. Bring it to a boil, then turn the heat to low and let it simmer for 30 minutes. After simmering, drain off the water, saving ½ cup of the ginger cooking liquid.
Return the ginger to the pot. Add the reserved ginger water, the granulated sugar, and the salt. Bring it back to a boil, then lower the heat to medium and cook for 35 to 40 minutes, stirring occasionally. The syrup should reach 225 degrees F on a candy thermometer.
Drain the ginger in a colander placed over a bowl so you can keep the syrup if desired. Spread the ginger on a cooling rack set over a cookie sheet. Separate the slices and let them dry for about 2 hours. They should feel sticky but not wet.
Place the sticky ginger slices in a bowl of sugar and toss until coated. Arrange them back on the rack and let them dry overnight.
Once fully dry, store your candied ginger in an airtight container in a cool, dark place. It keeps for several months and can be frozen for at least 6 months.